The invention concerns a method and apparatus for providing local time signals to a radio-controlled timepiece when a current location of the timepiece is outside of the range of a regional time transmitter.
The features of the general kind set forth are known from the article xe2x80x9cRadio-controlled timepiecesxe2x80x94Everyday timepieces of the 21st Century?xe2x80x9d by K. Baderschneider in the journal Uhren, Juwelen, Schmuck (UJS), issue 4/1989, beginning at page 182 (in particular at the end of the first column and the beginning of the second column on page 184). That article discloses that long-distance carriers such as aircraft, railways and buses, can emit time signals representing the respectively applicable local time in order to enable the passengers to set their radio-controlled wristwatches to the local time.
In particular it is proposed therein for air travel that time and position information of a global radio navigational system (for example OMEGA, LORAN, NAVSTAR, and GPS) be received by equipment on the aircraft. The current local time which is derived therefrom, by a processing step involving radio-engineering procedures, can be emitted by way of an on-board communication system on a technically convenient frequency, so that the passengers"" radio-controlled wristwatches, which are specifically designed for that purpose, then display the time corresponding to the instantaneous flight position. That proposal admittedly sounds promising but it is technically too expensive to be an attractive proposition in terms of price for consumers, having regard to the inevitably comparatively slight spread of such systems, especially because provision has to be made in one timepiece for receiving the signals of both a conventional stationary regional transmitter and an on-board transmitter.
It is known from DE 43 13 945 A1, for the purposes of spreading local normal time information, to use a large number of satellites which are on low polar orbits (so-called LEOS) as relay stations for a worldwide reference time, with the particularity that each satellite converts the time information which is to be radiated therefrom into the time zone which is associated with its polar orbit. Thus, on the ground, the local time is received directly from that satellite and displayed. However impressive that system seems, it nonetheless suffers from the practical disadvantage that the time zone changes involve, in principle, a gradation in each case of only 15 degrees of longitude while in actual fact the time zone boundaries extend along boundaries of countries or states. Thus for example at least three different time zones apply in South America along a strip of 15 degrees from South to North. Added to that is the fact that the acquisition areas of such telecommunication satellites overlap widely on the ground so that in most reception zones it is not possible to derive a clear association in respect of the geographical position with a given one of the satellites from the intensity of reception thereof. If however the receiving device, for example the wristwatch, is tuned to receive only one given satellite which is associated with that time zone, then once again there cannot be an automatic change in the local time display when travelling across time zones. Therefore, much more expensive means would have to be used for identification, at the receiving end, of locally associated satellites. Finally, particularly in the case of wristwatches, there is the fundamental difficulty of sufficiently reliably receiving the weak and very high-frequency satellite signals; at least, for that purpose there must be a free view of the heavens over a certain period of time, which is not readily ensured in the case of a low satellite orbit in densely populated areas or in mountainous countryside.
In principle, reception problems of that kind occur even with a higher satellite orbit as in the case of the navigational satellite systems referred to in the opening part of this specification. Those systems, in terms of receiving and displaying items of time information, also involve the additional problem of operating their own time base which does not run synchronously with the coordinated world time (GMT). For example, in the case of GPS, the time base does not contain either switching seconds or items of information relating to Summer time/Winter time change; and the time format is rather unsuitable for consumer purposes because it is only based on counting the weeks from Jan. 6, 1980 and the seconds within each week begunxe2x80x94with the additional limitation that time counting begins again at 0 after each 1023 weeks. Upon direct reception of an item of GPS time information with a consumer timepiece, therefore, a considerable amount of processing complication and expenditure must be implemented in the timepiece in order to convert the GPS system time into a correct world time, although this still does not always give a correct local time display.
In this respect, the dissemination of items of regionally correct time information by means of encoded signals on telegrams by way of regional long-wave transmitters such as in particular the transmitter DCF 77 at Frankfurt (Main) in Germany for dissemination of the official Central European Time has the inestimable advantage that, because of ground wave dispersion of the long waves and their capacity for penetration even into moderately well-screened spaces, practically everywhere in everyday life it is important to be able to sufficiently reliably receive the time telegrams even with miniaturized antennae and receivers in wristwatches. That applies in a large area of at least 1000 km radius, that is to say at any event over the region of a time zone. There is therefore only precisely the problem that the consumer does not see from his watch when he changes from one respective time zone to another when crossing the River Oder in the East or the English Channel in the West, because the continuing reception of the regional transmitter in Frankfurt still causes a display of the current Central European time.
Admittedly, regional time transmitters are operated in various regions of the Earth such as in particular in North America, in Great Britain and in Japan, which emit real-time telegrams in accordance with the local time of the location of the transmitter or in relation to the world time UTC. However, for the simple reason of avoiding interference phenomena which disturb operation thereof, each transmitter operates on a different frequency. In addition, the data format of the telegram encodings of the respective regional time transmitters is greatly different, so that even the complication and expenditure for frequency changing in the radio-controlled timepiece would still not be sufficient to ensure that, in the reception area of another regional time transmitter, the timepiece can automatically display the local time thereof.
In consideration of those factors and problems which relate in particular to the demand for a consumer radio-controlled timepiece which can be produced economically and which can be used without difficulty in any time zone, the object of the present invention is to provide for consumers, in regions in which regional time telegram transmitters cannot be received, a local time which is always directly accurate and which is derived from a time base available on a supraregional basis, such as in particular a satellite system or an Internet time provider.
In accordance with the invention that object is essentially achieved in that a conversion into the local time at the place of operation is effected in local satellite or Internet time receivers operated in a stationary or mobile mode, and that time information is then in turn radiated again in the format (that is to say at the frequency and with the encoding pattern) of a current regional time transmitter such as in particular the DCF 77, with a very low level of transmission powerxe2x80x94and thus receivable only in the close-range region.
That has a quite substantial advantage for the consumer that his radio-controlled clock which is tuned to reception of the domestic regional time transmitter can be operated practically anywhere in the world without any need for intervention, because, outside the time zone which applies in respect of that regional time transmitter, only locally-operated small-scale transmitters deliver a higher level of reception strength. Thus, when the consumer passes, his/her timepiece is set to the local time which is currently applicable there, for example after passing a motorway or expressway limit or border station or after alighting from a train at a railway border station.
The radio-controlled clock when thus once set to the locally accurate time then continues to run autonomously under quartz control until, in the same time zone, confirmation of the displayed timepiece time is received or, after the wearer of the timepiece travels farther into another time zone, a local close-range transmitter which is operated there supplies the local time which is applicable in that zone.
In order therefore always to permit an accurate local time display on a worldwide basis by means of conventional radio-controlled timepieces, it is proposed in accordance with the invention that close-range transmitters are operated locally with a minimum level of transmission energy. The transmitters would radiate, at the same frequency and with the same encoding as one of the established regional long-wave time transmitters, time telegrams which contain the local time information derived from a global satellite or Internet time base. In that way, consumer radio-controlled timepieces such as in particular alarm clocks and wristwatches can be operated worldwide although they are only designed for the frequency and encoding of a regional time transmitter such as the Central European long-wave standard time transmitter DCF 77.
Such a local time converter can therefore also be designed as a wireless Internet access, in order to obtain the information which is to be converted into locally applicable time telegrams, not primarily as items of positioning auxiliary information by way of a satellite antenna but already in date time format for example in accordance with the NTP-protocol from the WWW. This affords the advantages, for the functions of a position identifier or sender and possibly a time converter, of having recourse to computing and storage capacities of the Internet browser, and then, besides the local time information, also being able to transmit by way of the close-range transmitter further items of current information such as for example indications of the presence of fax or e-mail messages.